[test] Correctly merge expected test outcomes.

Without this change, wildcards always overwrite the outcomes
of more specific rules. Now we always merge.

Review URL: https://codereview.chromium.org/1153073002

Cr-Commit-Position: refs/heads/master@{#28629}

tools/testrunner/local/testsuite.py

@@ -150,7 +150,7 @@ class TestSuite(object):
         assert rule[-1] == '*'
         if testname.startswith(rule[:-1]):
           used_rules.add(rule)
-          t.outcomes = self.wildcards[rule]
+          t.outcomes |= self.wildcards[rule]
           if statusfile.DoSkip(t.outcomes):
             skip = True
             break  # "for rule in self.wildcards"

tools/testrunner/objects/testcase.py

@@ -34,7 +34,7 @@ class TestCase(object):
     self.path = path          # string, e.g. 'div-mod', 'test-api/foo'
     self.flags = flags or []  # list of strings, flags specific to this test
     self.dependency = dependency  # |path| for testcase that must be run first
-    self.outcomes = None
+    self.outcomes = set([])
     self.output = None
     self.id = None  # int, used to map result back to TestCase instance
     self.duration = None  # assigned during execution